Fluid containing endoluminal stent

ABSTRACT

An endoluminal stent contains a hollow passageway for the circulation of fluids to treat vascular walls affected with malignant growths or experiencing restenosis. The hollow passageway stent can have one or a plurality of passageways and is configured in a tubular shape with numerous coils, providing an empty tubular lumen through the center of the stent to allow blood flow. The stent is connected to a removable catheter that conducts fluid to the stent. Fluid flow may be regulated by valves incorporated in either the stent and/or the catheter. The stent and catheter are connected to avoid leakage of the fluid. Cryogenic, heated or radioactive fluids are circulated through the stent to treat the affected sites. A method of delivering drugs to the vascular wall is also provided by creating a stent with porous outer walls to allow diffusion of the drug.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional application No.60/105,768, filed Sep. 30, 1998, which is incorporated fully herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to endoluminal devices, and moreparticularly to stents.

2. Description of Related Art

Stents and similar endoluminal devices have been used to expand aconstricted vessel to maintain an open passageway through the vessel inmany medical situations, for example, following angioplasty of acoronary artery. In these situations, stents are useful to preventrestenosis of the dilated vessel through proliferation of vasculartissues. Stents can also be used to reinforce collapsing structures inthe respiratory system, the reproductive system, biliary ducts or anytubular body lumens. Whereas in vascular applications fatty deposits or“plaque” frequently cause the stenosis, in many other body lumens thenarrowing or closing may be caused by malignant tissue.

Fluids have traditionally been used to pressurize the angioplastyballoons used to open restricted vessels. The balloons may have avariety of shapes including a coiled form. In such a device fluid isinjected into the balloon to inflate the device and maintain turgidity.Shturman (U.S. Pat. No. 5,181,911) discloses a perfusion ballooncatheter wound into a helically coiled shape with one end attached to afitting and the other to a syringe for inflating the balloon with fluid.When the balloon is inflated, its coiled form allows blood flow thoroughthe open center of the structure. At the same time it is possible toactually have fluid flow within the balloon structure so that thesyringe can deliver fluid into the balloon, fluid can flow through theballoon, and fluid can then exit through a second lumen in a catheterattached to the syringe.

Coiled stents that are connected to a catheter apparatus, as in Wang etal. (U.S. Pat. No. 5,795,318), are used for temporary insertion into apatient. Wang et al. discloses a coiled stent of shape-memorythermoplastic tube that can be converted from a relatively narrowdiameter to a larger coiled form by heating. The narrow diameter coil ismounted at the end of a catheter over a balloon and in a preferredembodiment a resistive heating element runs down the length of thethermoplastic element. An electric current is applied to heat theelement thereby softening it while the balloon is expanded to enlargethe diameter of the coil. Upon cooling the enlarged coil hardens and theballoon is withdrawn. After the temporary stent has performed its duty,it is again heated and removed while in the softened state. In oneembodiment the thermoplastic tube is supplied with an additional lumenso that liquid drugs can flow into the stent and delivered throughapertures or semipermeable regions.

The attempt to kill or prevent proliferation cells is a common theme inclinical practice. This is generally true in vascular and non-vascularlumens. It is known that ionizing radiation can prevent restenosis andmalignant growth. Although the effect of temperature extremes, e.g.,cryogenic (cold) or hot temperatures, on cellular activity is not aswell researched, it may provide a safer approach to control of tissueproliferation. Among the drawbacks of the prior art coiled balloons isthat the balloon material is relatively weak so that expansion andcontraction cause the balloon to fail. Failure of a balloon containingradioactive or cryogenic fluids could be catastrophic. It would bedesirable to provide a catheter based, minimally invasive device forstenting support that could deliver hot or cryogenic or radioactivefluids or drugs and that would be sturdy and could remain in the bodyfor extended periods of time, detached from the insertion device.

SUMMARY OF THE INVENTION

In its simplest embodiment the present invention is an endoluminal coilstent comprising a hollow tube formed into a series of loops or otherknown stent shapes which initially has a low profile and diameter. Thisstructure can be delivered into a patient's vascular system and expandedto full size. The present invention to provides a stent that is hollowallowing the passage of fluid. The stent has either one or a pluralityof passageways for fluid flow. The stent is attached to a catheter via aspecial fitting so that when engaged with the catheter, fluid flowsfreely from the catheter to the stent with a possible return circuitthrough the catheter. When disengaged, the fitting prevents leakage fromthe stent permitting the stent to remain in place in a patient'svasculature.

This invention provides a way of treating vascular areas affected withmalignant growths or experiencing restenosis from smooth muscle cellproliferation, etc. The stent is inserted in a small diameterconfiguration and after being enlarged to a larger diameter, acts as asupport device for the areas of restenosis or malignant growth. Inaddition, the stent can treat these affected areas in a unique way byflowing radioactive, heated or cryogenic fluids through the stent.

The present invention also provides a way of delivering drugs to anaffected site. A stent to accomplish this purpose can be composed ofseveral different materials. For example, the stent can formed from ametal or other material with small pores machined or otherwise formed(e.g., with a laser). When such a stent is filed with a drug, that drugslowly disperses through the pores. Alternatively, an entire metal tubeor portions of the tube could be formed e.g., from sintered metal powderthereby forming a porous structure for drug delivery. Another embodimentwould alternate a metal tube (for structural stability) with dispensingsegments inserted at various intervals. The segments would be perforatedto allow seepage of the drug or would be otherwise formed from a porousmaterial. Another embodiment employs an expanded polytetrafluoroethylene(PTFE) tube around a support wire or metal tube in the form of a coiledstent so that a hollow passageway is created between the metal and thePTFE. A drug is flowed into this space and slowly dispensed through theporous PTFE.

One embodiment of the hollow stent of the present invention comprises ashape memory metal such as nitinol. Shape memory metals are a group ofmetallic compositions that that have the ability to return to a definedshape or size when subjected to certain thermal or stress conditions.Shape memory metals are generally capable of being deformed at arelatively low temperature and, upon exposure to a relatively highertemperature, return to the defined shape or size they held prior to thedeformation. This enables the stent to be inserted into the body in adeformed, smaller state so that it assumes its “remembered” larger shapeonce it is exposed to a higher temperature (i.e. body temperature orheated fluid) in vivo.

Special fittings are incorporated at the ends of the hollow stent. Thesefittings facilitate the injection and removal of fluid and also allowthe stent to be detached from the insertion device to be left in placein a patient. The hollow stent has an inlet and an outlet so that acomplete fluid path can be created, and fluid can be continuallycirculated through the stent. In the simplest configuration the inletand outlet are at opposite ends of the stent. However, if the stent isequipped with a plurality of lumens, two lumens can be connected at adistal end of the structure so that the outlet and inlet are bothtogether at one end. Other arrangements can be readily envisioned by oneof ordinary skill in the art.

The stent is inserted into the body while connected to a catheter in asmall, deformed state. Once inside the patient's body the stent isadvanced to a desired position and expanded to its larger full size. Ifthe stent is composed of shape memory metal, for example, the stentexpands from its small-deformed state to its remembered larger state dueto the higher body temperature or due to the passage of “hot” fluidthrough the stent. Subsequently “treatment” fluid (e.g., heated,cryogenic or radioactive) is pumped through the catheter to the stentwhere it is circulated throughout the stent, treating the adjacentvascular walls. The catheter can either be left in place for a certainperiod of time or removed, leaving the fluid inside the stent. Thiswould particularly be the case with radioactive fluid or with a porousdrug delivery stent.

The stent can be removed by reattaching the catheter allowing one tochill and shrink the stent (in the case of a memory alloy).Alternatively, the device can readily be used in its tethered form toremove memory alloy stents of the present invention or of prior artdesign. For this purpose a device of the present invention is insertedinto the vasculature to rest within the stent to be removed. Warm fluidis then circulated causing the stent to expand into contact with thememory alloy stent that is already in position. At this point cryogenic(e.g., low temperature) fluid is circulated causing the attached stentand the contacted stent to shrink so that the combination can be readilywithdrawn.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hollow coiled stent.

FIG. 2 is a perspective view of a valve assembly to be used with FIG. 1.

FIG. 3 is a sectional view of the hollow stent tube of FIG. 2.

FIG. 4 is a representation of the stent of FIG. 1 in the position fortreatment.

FIG. 5 is a sectional view of a second embodiment of a hollow coiledstent.

FIG. 6 is a perspective view of a second embodiment of a hollow coiledstent.

FIG. 7 is a perspective view of a third embodiment of a hollow coiledstent.

FIG. 8 is a perspective view of a valve assembly to be used with FIG. 6.

FIG. 9 is a perspective view of a fourth embodiment of a hollow coiledstent.

FIG. 10 is a sectional view of the hollow stent tube of FIG. 8.

FIG. 11 (11 a, 11 b, and 11 c) is an illustration of the method detailedin FIG. 12.

FIG. 12 is a flow diagram explaining use a stent of the presentinvention to retrieve a shape memory stent already in place.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, in which like reference numbers representsimilar or identical structures throughout the drawings, FIG.1 depicts apreferred embodiment of this invention. Pictured in FIG. 1 is a medicalapparatus 10 comprising an endoluminal stent 20 attached to a deliverycatheter 30 by means of a valve assembly 40. In this representationendoluminal stent 20 is generally coiled in shape leaving a tubularspace down the center of its length. Obviously, the principle of ahollow stent can be applied to stents of a zigzag or other constructionother than simply coiled. The tubing 22 of the stent 20 is preferablycomposed of a metal material that can be crimped onto a balloon catheter(not shown) for insertion into a body. Once positioned inside of thebody at the desired location, the balloon can be inflated, bringing thestent from a compact small size to its enlarged full size thus opening apathway for blood flow.

Inside the tubing 22 of stent 20, two fluid pathways exist. Thesepathways can be seen in the cross sectional view of FIG. 3. Pathways 26and 28 have opposite flowing fluid streams and connect at the distal end24 of stent 20. By allowing for opposite streams, radioactive, heated orcryogenic liquids can continuously flow through stent 20 for the purposeof killing or preventing proliferation of cells. By “heated” or “hot” ismeant temperatures above body temperature. By “cryogenic” or “cold” ismeant temperatures below body temperature. The stent 20 can eitherremain connected to a delivery catheter 30 for temporary insertion, orbe detached for a more permanent insertion. In either case, fluid flowcan be circulated throughout stent 20 prior to disconnection. In thesimplest design, fluid passageways connected to the stent 20 are lumensof the delivery catheter so that when the catheter is withdrawn, fluidflow must cease. It is also possible to provide separate flexible tubesthat are threaded through the catheter so that the delivery catheter canbe withdrawn leaving the relatively smaller fluid delivery tubes (notshown) behind. Preventing leakage of the fluid from the stent 20 afterthe catheter 30 is disconnected is accomplished through a valvemechanism contained in the catheter 30, or the stent 20 and/or both. Inthe example illustrated in FIG. 2 rubber or elastomer diaphragms 25 arepenetrated by small hollow needles 48 in the valve assembly 40. Inaddition, the valve 40 may comprise a simple back flow preventer. Thus,when pressure is applied from incoming fluid to the valve assembly 40, aball 45 which sits in a ball seat 44 is forced back against a spring 46and the valve 40 opens for the incoming fluid pathway 28. A similararrangement allows pressure to open the outgoing fluid pathway 26. Acheck ball valve is shown only as an example. Flap valves or any of anumber of other back flow valve designs well known in the art can beemployed. Complex systems in which a bayonet-type attachmentautomatically opens a valve are also possible.

The catheter 30 comprises a catheter shaft 32, which further containstwo fluid pathways 34 and 36 as seen in FIG. 2. At the distal end ofcatheter 30, the valve assembly 40 has small hollow needles 48 that aredesigned to puncture elastomer diaphragms 25. The catheter 30 isslightly larger in diameter than the stent member 20 so that thecatheter tubing wall 32 forms a friction fit over the stent wall 22.This creates a seal between the catheter 30 and the stent 20 for fluiddelivery and removal. Upon detaching the catheter 30, leakage from thestent 20 is prevented due to the self-healing properties of thediaphragms 25. Obviously, the back flow preventer 40 could be on thestent 20 and the diaphragms could be on the catheter 30.

As discussed above, stent 20 is inserted into the body to the desiredsite through the use of a catheter insertion device well known in theart. FIG. 4 depicts stent 20 in its enlarged form after it has beeninserted into the body at the affected location and expanded. Othermeans of stent expansion other than a balloon catheter are possible. Ifthe stent 20 is formed from shape memory metal, such as nitinol, theheat of the body can cause the stent 20 to assume a larger, rememberedform. Alternatively, heated fluid can be circulated through the stent tocause it to recover its remembered form. A self-expanding stent made ofa spring-type alloy can also be employed. In that case the deliverycatheter would be equipped with means (e.g., an outer sheath) to keepthe stent compressed until it was at the desired location.

By increasing the diameter of stent 20 at an affected location, thepassageway is enlarged to permit increased blood flow. At the same time,fluids can pass through the interior of tubes 22 of the hollow stent 20to treat the vascular wall. The walls of the vasculature can be treatedby running either a radioactive, cryogenic or heated fluid through thestent 20 or by delivering a drug through a stent equipped for drugdiffusion (e.g., through holes or a porous region).

FIG. 5 depicts a second embodiment of the invention. In this embodiment,the hollow stent 60 has only one fluid pathway 66, an inlet without anoutlet, and is used to deliver drugs to affected areas. Once the stent60 is inserted into place and is in its enlarged configuration, drugsare delivered through the catheter to the stent 60. Stent 60 can beconstructed in various ways to facilitate the delivery of drugs. In onecase, as shown in FIG. 6, the stent 60 is constructed with regions orsegments that have pores 64 to allow drug seepage from the tubing 62.Alternatively, continuously porous metal, porous plastic, or acombination of metal and plastic can be used. The perforations 64 orslits in the stent to facilitate drug delivery must be of sufficientlysmall size to allow the passage of the drug through the entire length ofthe stent so that all areas can be treated. It will be apparent thatpore size can control the rate at which the drug is dispensed. It ispossible to cover the pores 64 with semipermeable membrane to furthercontrol and restrict drug outflow. A semipermeable membrane withinclusion of an osmotic agent with the drug will result in water uptakeand more rapid and controlled pressurized delivery of the drug.

A third embodiment of the invention, FIG. 7, has a hollow stent 70containing a single fluid pathway. The tubing 72 can be made of any ofthe materials discussed above, but in this embodiment, the stent 70 hasan inlet path 78 that carries the fluid to the distal end 74 of stent 70where it then runs through the coils. In this embodiment, a valve 80connects the stent 70 to catheter 30. FIG. 8 shows a cross-sectionalview of valve 80. The pressure from the liquid sent through the cathetercauses the gate 82 of valve 80 to open to allow the fluid into the inletpath 78. The pressure that forces the opening of gate 82 causes thesimultaneous opening of gate 84, allowing the fluid that is circulatedthrough the stent 70 to exit through pathway 36 of catheter 30. Thefluid entering and exiting through catheter 30 must also go through acheck ball valve assembly similar to the one shown in FIG. 2. Again,flaps or other “one way” valve mechanisms can be applied. After allincoming fluid has been delivered to the stent 70, the absence ofpressure causes gate 82 and gate 84 to close, thereby closing valve 80.This design can be used with any of the fluids mentioned above. Thestent 70 can be used to circulate radioactive or cryogenic fluids fortreatment of the vascular walls and can also be perforated for thedelivery of drugs.

In a fourth embodiment, a hollow coiled stent 90 is formed frompolytetrafluoroethylene (PTFE) 92. In FIG. 9, a perspective view of thisembodiment can be seen. The stent 90 consists of a support wire 94 overwhich PTFE 92 is fitted. The pliable structure resulting is then formedinto a coiled stent. The PTFE 92 is fitted around the wire 94 so thatthere is sufficient room to allow the passage of fluid. FIG. 10 shows across-sectional view of stent 90, illustrating the pathway 96 createdaround the support wire 94 to allow the passage of fluid. In thisembodiment, stretched expanded PTFE can be used to create a porous stentto facilitate the delivery of drugs. The wire 94 can also be hollow(passageway 95) so that the stent 90 can simultaneously deliver drugsand radioactive fluid or temperature regulating fluid.

A fifth embodiment of the invention is illustrated in FIG. 11 anddescribed in a flow diagram shown in FIG. 12. This embodiment is amethod for recapturing an existing shape memory metal stent already inthe body. With reference to both FIGS. 11 and 12, a shape memory metalstent A is inserted into the body in its small, deformed state throughthe use of an insertion device well known in the art in step 112. Theinserted stent A in its deformed state is placed into the center of amemory alloy stent B that is already in an enlarged support position inthe body in step 114. The deformed stent A is then enlarged so that itcomes in contact with stent B. This can be accomplished in one of twoways. Either the stent A may enlarge due to the higher in vivo bodytemperature in step 115, or a hot liquid may be pumped through stent Ato cause it to expand in step 116. Once expanded and in contact withstent B, cryogenic liquid may be pumped through stent A so that bothstent A and stent B are chilled and either shrink down to their deformedstates or become sufficiently relaxed to allow ready removal in step118. Once in a small, deformed or relaxed state, stents A and B areeasily removed from the body in step 119 by withdrawing the catheterattached to stent A. FIG. 11a illustrates stent A in its reduced statebeing inserted into stent A. FIG. 11b shows an enlarged version of stentA contacting stent B. Thereafter, a temperature change caused, forexample, by fluid circulating through stent A will shrink both stentsand enable their removal (FIG. 11c).

Having thus described a preferred embodiment of a hollow endoluminalstent, it should be apparent to those skilled in the art that certainadvantages of the within system have been achieved. It should also beappreciated that various modifications, adaptations, and alternativeembodiments thereof may be made within the scope and spirit of thepresent invention. For example, a hollow stent with a coiled, tubularshape has been illustrated, however, many other possibilities exist forthe shape and size of the hollow stent. In addition, the passageways areillustrated as round but could take on a variety of other shapes. Thedescribed embodiments are to be considered illustrative rather thanrestrictive. The invention is further defined by the following claims.

I claim:
 1. An endoluminal stent system comprising: a stent comprised ofnon-inflatable non-porous tubing, having at least one fluid flow conduittherein, wherein the tubing is circumferentially arranged so as to forma side wall of the stent, thereby creating a main lumen of the stentthrough which blood can flow; a removable catheter wherein a proximalend remains outside of a body and a distal end is sealingly attached tothe stent, wherein the catheter is adapted to deliver fluid to thestent; connector means for attaching the removable catheter to thestent; and valve means within the system for controlling fluid flow. 2.The endoluminal stent system as described in claim 1, wherein the stentis formed from metal.
 3. The endoluminal stent system as described inclaim 2, wherein the stent has shape memory properties.
 4. Theendoluminal stent system as described in claim 1, wherein the stent isformed from plastic.
 5. The endoluminal stent system as described inclaim 1, further comprising a core that is positioned within, but spacedapart from, an outer wall of the tubing, creating an annular regiontherebetween.
 6. The endoluminal stent device as described in claim 5,wherein said core contains a hollow passageway.
 7. The endoluminal stentsystem as described in claim 1, wherein the tubing is formed into acoiled structure.
 8. The endoluminal stent system as described in claim1, wherein the tubing has a circular shape in cross-section.
 9. Anendoluminal stent device comprising: a stent defined by a non-inflatablenon-porous outer wall adapted to accommodate a fluid therein, whereinthe outer wall is arranged into a coiled structure so as to form a sidewall of the stent, thereby creating a main lumen of the stent throughwhich blood can flow; a removable catheter wherein a proximal endremains outside of a body and a distal end is sealingly attached to aconnector, wherein the catheter is adapted to deliver fluid to thestent; and valve means within the device for controlling fluid flow. 10.The endoluminal stent device as described in claim 9, wherein said valvemeans are contained within said stent.
 11. The endoluminal stent deviceas described in claim 9, wherein said valve means are contained withinsaid catheter.
 12. The endoluminal stent device as described in claim 9,wherein the stent is formed from metal.
 13. The endoluminal stent deviceas described in claim 12, wherein the stent has shape memory properties.14. The endoluminal stent device as described in claim 9, wherein thestent is formed from plastic.
 15. The endoluminal stent device asdescribed in Claim 9, further comprising a core that is positionedwithin, but spaced apart from, the outer wall of the stent, creating anannular region therebetween.
 16. The endoluminal stent device asdescribed in claim 15, wherein said core contains a hollow passageway.17. The endoluminal stent device as described in claim 9, wherein theouter wall has a circular shape in cross-section.
 18. An endoluminalstent apparatus comprising: a stent comprised of a support wiresurrounded by an expanded polytetrafluoroethylene tubing, creating afirst lumen therebetween, wherein the combination of support wire andexpanded polytetrafluoroethylene tubing is arranged into a coiledstructure so as to form a side wall of the stent, thereby creating amain lumen of the stent through which blood can flow, wherein the tubingincludes a plurality of porous segments spaced apart from each otheralong a length thereof, and wherein the support wire is hollow, creatinga second lumen coaxial with the first lumen; and a removable catheter,wherein a proximal end remains outside of a body and a distal end issealingly attached to the stent, wherein the catheter is adapted todeliver fluid to the stent.
 19. The endoluminal stent apparatus asdescribed in claim 18, further comprising connector means for attachingthe removable catheter to the stent.
 20. The endoluminal stent apparatusas described in claim 18, further comprising valve means for controllingfluid flow in the system.
 21. The endoluminal stent system as describedin claim 1, further comprising two fluid flow conduits, wherein saidconduits are distinct and separate at a proximal end of the stent, andwherein said conduits are connected at a distal end of the stent. 22.The endoluminal stent device as described in claim 9, further comprisingtwo fluid conduits, wherein said conduits are distinct and separate at aproximal end of the stent, and wherein said conduits are connected at adistal end of the stent.